If there is large-scale out-migration of people aged 20-34 from a region while the absolute numbers of children and elderly people remain nearly constant, what is the most likely effect on the total dependency ratio?

Correct answer: It will rise because the working-age base becomes smaller

The total dependency ratio compares dependent people with the working-age population. In a common form, it is \(Dependency\ Ratio=\frac{Children+Elderly}{Working\text{-}age\ population}\times100\). If many people aged 20–34 leave, the denominator becomes smaller. If the numbers of children and elderly people remain nearly unchanged, the numerator stays nearly the same. A similar numerator divided by a smaller denominator produces a higher ratio.

Therefore option B is correct. The fact that total population falls does not mean the ratio falls, because the departing people are mainly from the working-age group. Option C overlooks the reduced denominator, and option D is impossible while dependents remain. The result assumes the stated age groups represent the working-age base and that other changes are small.